Correcting ocular defects



May 24, 1938. AAMS, JR, ET AL y 2,118,132

CORRECTING OCULAR DEFECTS y Filed oct. 2e, 19:54 4'sneets-sne'et 2rCoA/CA VE fili ,B

L25 www CONVEX COA/CAVE je N, 222W Y May 24, 1938. A. Amas, JR.. Er AL2,118,132 v CORRECTING OCULAR DEFECTS I Filed oct. ze, 1954 4sheets-sheet s May 24, 1938.

A. AMES, JR., El' AL CORRECTING OCULAR DEFECTS w Filed OCT.. 26, 1934 4Sheets-Sheet 4 immmmw' v Y Patented May 24, 193s UNITED STATES CORRECTmGOCULAR'DEFECTS Adelbert Ames, Jr.,Gordon H. Gliddomand Kenl f neth N.Ogle, Hanover,

N. H., assignors to Trustees of Dartmouth College, Hanover, N. H., acorporation of New Hampshire Application October 26, 1934, Serial No.750,162

v y12 claims. (ci. fis-54) l the patient to see `two objects where inreality Heretofore, various defects ofthe eyes have been known andcorrected in different ways appropriate to these defects. For example,dioptric errors have been corrected by spherical, cylindrical or toriolenses, and muscular defects or phorias by means of prism lenses whichaffect the vergence of the eyes by changing the direction of the line ofsight of an eyeball when the ocular muscles fail to turn it correctly.

More recently, a hitherto not investigated but quite common eye defecthas been found which will be referred to as aniseikoniav and involvesdiierences in size and/or shapeof the ocular images in binocular vision,also referred to as eikonic conditions. The term ocular image describesthe impression formed inthe higher brain centers through the vision ofone eye. It isA determined not only by the properties of the dioptricimage that is formed in the retina of the eye, but also by themodifications imposed upon that image by the anatomical properties andphysiological processes by which this image is carried to the higherbrain centers.

Methods and instruments forl evaluating aniseikonias are for exampledescribed in the Patent No. 1,944,871 of January 30, 1934 to AdelbertAmes, Jr. and Gordon H. Gliddon', and in the Patent No. 1,954,399 ofApril 10, 19,34 to Adelbert Ames, Jr. Spectacles for correctinganiseikonias, also referred to asl iseikonic spectacles, have also beendeveloped and are described for example in the Patent No. 1,933,578 ofNovember 7,' 1933 to Adelbert Ames, Jr. and Gordon H. Gliddon. Suchiseikonic spectacles change the magnification to a predetermined degreeand may or may not have in addition a .specifieddioptric effect. nAniseikonia may be of the so-called overall type in which one image islarger than the other in all meridians, or it may be meridional, whereone image is larger than the other in one meridian. Meridionalaniseikonia may be uniform with respect to that meridian, or it may havethe form of distortional disparity along that meridian, principally thehorizontal one?.

Disparities of the latter type correspond to the effects of prisms,which distort an image in the meridian in which they bend the line ofsight. Therefore, prisins can be used for compensating or rectifyingsuch distortional aniseikonias. However, ordinary prisms used forcorrecting this defect would change the -vergence of the eyes andintroduce a new defect equivalent to muscular defects as phoria ortropias tending to cause there is only one. Y It is therefore one of theobjects of this invention-,to provide a method and meansfor correctingdistortional aniseikonia by distorting the image` formed on the retinaof .an eye without changing the direction of the line of sight'.

Such means, however, which could introduce corrective distortion withoutunwanted change` of vergence, would in many cases change the dioptricand/or overall and meridional magnication properties of the eyesintroducing thereby these types of aniseikonia. It is,`therefore,another object of this invention to provide methods and means forcorrectively distorting the image formed on the retina o! an eye, whileat the same time controlling the dioptric and/or overall and uniformlymeridional eikonic properties o1' the eyes.`

If prisms are used to correct phoria only, `no distortional aniseikoniabeing present, the distortional effector the prisms introduces thelatter defect to the disadvantage of the wearer. Our invention permits,in another'aspect thereof, a change of vergence, or direction of lineso! sight. without distorting theimage, or by introducing apredetermined. amount of distortion and at the same time, if required,controlling the dioptric, andeikonic conditions.

In its general aspect, the invention has therefore the object ofproviding a method and means for evaluating or correctingphoria anddioptric defects, and overall, meridional and distortional aniseikoniao1' the eyes, whereby any one, several, or all of these defects may beinherently present, `or introduced by correcting one, orseveral of theother defects.

These and other objects, features and aspects of our invention will beapparent from the 1'ollowing detailed explanation thereof illustratingvits genus with reference to general practical embodiments. Thedescription refers to drawings in which: i

Fig. 1 is a schematical representation .of the distortion effect of aprism;

Fig. 2 is a diagram showing the relation between distortion andmagnicationzof a prism;

Figs. 3 to 6 are .diagrams explaining the effect of prisms upon thehoropter;

Fig. '7 is a diagrammatical representation of apparatus for carrying outpartition measurep ments; f

Figs. 8 and 9 are diagrams giving the relations between distortion,vprism power and base cuve;

Fig. is a plan view, partly in section, showing a spectacle frame inwhich is mounted one embodiment oi our invention;

Fig. 11 isa vertical cross-section of Fig. 10 l taken along line II-Ilthereof;

Fig. 12 is a diagrammatic view illustrating the method of designing adistortionless prism;

Fig. 13 is a vertical cross-section of a slightly modiiled form of ourinvention; lo Fig. 14 is a horizontal cross-section of the de- .viceshown in Fig. 13, taken along the line Il-M thereof;

Fig. 15 is a diagrammatic illustration showing our invention in positionbefore aneye;

Yu Fig.4 16 is an elevation of the principal lensused in trying out ourinvention; Pig asis a front elevation view, showing a spectacle frame inwhich `is mounted oner eni- .bodiment of our invention; l fn Fig. 181i:a cross-section oi Fig. 17 taken along line Il`-'-|lthereof;

Fig. 19. is a cross-section o1' Fig.,17, taken along line Irl-. .k-IQthereof; l y I Figfm isl a'partial sectional view similar to g5 Fig.iggshowing'a modification; k

Figa-121 yis a cross-section of Fig. 20; taken along line 2lb- 2ithereof;

Fig,;22fls a view similar to Fig. 20, showing anotherfmodiflcation; nFig. 23 'is a cross-section of Fig. 22, taken along line 23"-2I`thereof;Y Fig. 24 is a diagrammatic illustration showing one embodiment of ourinvention in position'before an eye; and j Figs. v25 and 26 show lenscombinations accordv ing to Tables V1I.a.n d V'lII.` f y For a betterunderstanding of the invention, the distortion eii'ected by prisms, andthe distortional aniselkonic defects 'of the eyes .will iirst o bediscussed.l

The distortion of an eyeglass'for a given iixation distance will hereinbe understood. to mean the change in the per cent magniication oi' theeyeglass for increasingperipheral angles. Anal- 5 ogously, it will bethe change inthe per cent .difference'in the angular size of the kobjectand the image produced `by'the eyeglass, reckoned from the anteriornodal point of the eye, for increasing values oi' the angularsize of-theobw ject. Thus, for a distortionless lens this change will be kzero,while fora pin-cushion distortion it will vary, increasing with ytheincrease in the angular size of thevobject.

Y 'I'he type oi' distortion 'exhibited by prisms in a the plane of thedeviation is, within about of the deviation, that of a constant changeasv indicated in Fig. 1, where O is an object in the form. of 'a dividedsquare, which appears distorted-as shown at O if viewed through a prism00 P. It will be evident that meridian d, and similarly any inclinedmeridian, is distorted as indicated at d. Thus, as graphically shown inFig. 2, the distortion vof a prism P will Vberepresented by anapproximately straight line D 66 (related to the position of the prismas indicated in Fig.v 2) in a system. coordinates representingmagniiicationv l,l and oblique angles qb, (see Fig. 3) respectively.magnitude of the disvtortion, above denedfps the change in per cent 70magnification per do'ree and herein called Y 7g is then graphicallyexpressed by the slopel oi the cipally in the horizontal meridian)vcausing the 10` above-mentioned distortlonal aniseikonia is,'gen ferally speaking, of the same nature as the just described distortioneffected by prisms. It is further afact that, in binocular vision, themagnitude of the two ocular-image distortions deter- 15 mines the shapeof the longitudinal horopter.

The horopter, which may be dened as the surface in space, every point onwhich is imaged on corresponding retinal points, is substantiallysymmetrical with respect to a'vertical plane through 20 the medial lineof sight of a 'person having no'y eikonic defects. If, however, theocularimages or portions thereof have di'ierent sizes, one and the sameobject appears smaller to that eye which produces a morev extendedocular image. This causes in binocular vision an apparent change inlocation and/ or shape of the object. For example, a4 diierence inoverall size of the ocular images produces a rotation ofthevlongitudinal horopter, which may be describedas the intersection oi thehoropter surface and fans of projection lines Afrom they m'ean nodalpoints of the eyes, these fans being coniined in ahplane through thesenodal points. 'Ihis rotation of the longitudinal horopter appears totake place about a vertical axis passing through the point of fixationat which the eyes are looking, the horopter portion at the side of theeye with the larger ocular image appearing more distant.

Fig. 3 indicates the location of the longitudinal 40 horopterof a personwith normal eyes, H being thev horopter4 trace (which may be for acertain visual distance b a straight line), and F a fixation point',determining vergence, at the distance b from R and L, the right and lefteyes, respectively,

of the observer. Fig. 4 shows the location of the horopter trace H1 if,under otherwise similar conditions, the ocular image of the left.eye islarger, A due to the interposition of a size changing lens S before thateye, orto a corresponding pathological diierence of the Ocular images.

Distortional` aniseikonias, either inherent or introduced by prisms,have theeil'ect of apparently curving the horopter, in a mannerindicated in Figs.V 5 and 6, Where H2 and Ha are the longitudi'- u nalhoropter traces apparent to normal eyes due to prisms P2 `and P3,respectively. Abnormal eyes havingv'a corresponding distortionalaniseikonia produce a similar eiect'. Defects of this type' can bemeasured with instruments of the general type described in theAabove-mentioned Patent No. 1,954,399. A patient having aniseikoniaexemplied in Fig. 5 would move the points of a horopter instrument toactual positions indicating trace H', in order to see them apparentlyplaced as indicatedA by ytrace H". By placing before the patients eyesdistorting prisms which produce coincidence of apparent horopter andactual horopter instrument setting, that is, which move H' and H", itispossible to correct this defect which, even if present 'only to a verylow degree, may cause serious illness.

A convenient way to measure distortional aniseikonia quantitatively isthe so-called Multiple 75 of changes of the ocular Partition Test" whichis based on the same principle as the horopter experiments, and which isconducted as follows: A series of object points represented by threadsor wires are arranged so that, as seen by each eye, all appear` equallyseparated directionally. As shown in Fig. '7 in oblique projection, a.series ofwires W, W1, W2, etc., and W1 and Wn, etc., respectively, isplaced before each eye. Wire W serves as a fixation object and may beiixed, as well as W1 and W1, the distances W, Wi and Wr being keptconstant. The other wires are laterally movable and the patient, lookingat W, W1, W2, Wa, W4, Ws with the right eye adjusts the wires so thatthey appear to bc equally spaced. If he has a distortional defect,thewires will actually be unequally spaced, and their positions provide ameasure of the amount of distortion, which can be checked with the aidof prisms correcting the defect. The other eye is similarly examinedwith Wires W, Wr, Wu, etc., and the combined effective distortion ofboth eyes must correlate with the unbalanced distortion of the horopter.

The shape of the longitudinal-horopter, then, is a measure of theunbalanced distortion between the ocular images of the two eyes in thelongitudinal meridian. Hence, the unit describing the distortion ofprisms should be of the order images for corresponding changes of thelongitudinal horopter.

Thus, the unit of prism distortion may be defined to signify 0.1%vvmagnification change per one degree peripheral angle.` A prism having aunit of distortion when placedV before one eye of an ideal observer at adefinite fixation distance, would cause the horopter trace of zero orunbalanced 4distortion (also called Vieth-Mller circle), to recede tothe frontal plane. Now in horopter theory, the distortion is defined asthat-is the change in magnification per tangent of peripheral angle, andh=2a/ b when the longitudinal horopter lies in the frontal plane, where2a will be the interpupillary distance and b the distance from themedian nodal point oi the two eyes to the point of fixation. If theabove ideal observer is assumed to have an interpupillary distance ofmm. and if his hcropter race is to be taken at l m. distance from theeyes (compare Fig. 3), then the value of h for this change is for thevalues given above It will now be evident that conventional. prisms used for correcting vergence (phoria efects may introduce eikonicdisturbances andthat, on

the other hand, conventional prisms used for correcting distortionalaniseikona would most likely cause a cha-nge in the relation of thelines of sight of the eyes equivalent to phorias. There i of bothdistortionally eikonic and muscular defects, and therefore `control ofboth distortion and deviation of the lines of sight by optical means.Inaddition; it may'beuneessary to correct dioptric defects andw'eikonicdefects other than distortion.- y

According to our invention, we` control the effect of lenses includingprism elements `by appropriately curving or bending prism compo nentsand, yif desirable, combining them with other prism components and/0rlens elements not directly influencing the direction of the lineoisight.I M

For purposes ofour invention, it is necessary to correlate ythe variouscharacteristics of optical prisms. While this can be done analytically,`it was found that a more convenient way, 'at least for preliminary or.approximate computations. is to relate these characteristicsgraphically, as will now be described. f

With the above discussed unit for the prism distortion ha, theproperties of prisms have been laid down graphically as shown in Figs. 8and 9. The effect of a prism depends'principally on prism power,curvature (that is the basev curve upon which the prism is ground),thickness of the prism, distance of prisinffrom eye, anddegree oftipping with respectto the visual axis.

In these graphs, the distortion ha (already defined as the change in percent magnification per unit peripheral angle) is plotted against thebase curves B in diopters, for various prism powers A. As minus basecurves are indicated Athose which .result in lenses concaveto the eye,4and asA plus ba'ses those which result in yocular surfaces convex tothe eye. Intermediate prism powers are omitted for the sake of clarity.The curves are drawn for a distance of about 23 mm. from the anteriorprism surface to the nodal point of the eye, that surface being alwaysperpendicular to the line of sight. Fig. 8 showsthe relations forinfinite or relaxation kvisual distance (that is, the distancebetweenfnodal'point and theobserved object), to which a distance of Labout 6 m. is practicallyequivalent, and Fig. 9 is similarly drawn for`reading distance, of about 40 cm. For the sake of practicalconvenience, the curvesr are made up for a constant trim (t' of Fig. 1loffrabout 1 mm. and varying center.

thickness t, but could also be computed vfor conare also intermediatecases requiring correctionv stant t. Similarfcharts can be made up fordify ferent distances from the eye to the prism.

These graphical representations of prism characteristics which, asalready pointed out, are especially convenient for purposes .of thepresent invention, can be obtained empirically by actually measuringprisms, or by conventional tri- 1 angulaton ray tracing methods wellknown in the art of optics.

While our invention provides for general c ontrol of distortion,deviation of the line of sight` and dioptric and eikonic defects byappropriate,- ly bending prism elements and in certaini in-v stancescombining them with other similar or different optical elements, twoespecially significant embodiments thereof are the correction ofdistortional aniseikonia without affecting the lines of sight, and ofdiverting the latter for corrective purposes, without introducingdistor`4 tion. The latter isthe simplest ymodification which may becalled Distortionless Prism` and f will first be described. Prisms ofthisl type are especially valuable in phoria cases which could a convexcurvature of 52.6714 mm. radius not be corrected with conventionalprisms becauseof the distortion thereby introduced.

In Fig. 10 there is shown a spectacle frame consisting of a pair ofdouble rims l for holding the lenses, a bridge member 2 connecting vsaidrims, and a pair of temples 3, hinged at 4 to endpieces 5, which are inturn secured to portionsof the rims I remote from the bridge 2. Y

It will be obvious that any suitable well known form of lens holdingmeans may be used, or that a special type of frame may be designed iffound necessary, the spectacle frame illustrated being' shown byy way of'example only. Also, it is in certain instances possible to join thelens elements directly, for example by cementing, and to mount them'in amore conventional frame..

As will now be *evident from the preceding discussiony of the relationof prism power, base curve and distortion, it is possible to nd prismshaving a'particulary curvature in the plane of the base-apex line asshown at 'l and 8 on the lens 6 of Figs. 10 and 11, which prisms bendthe. line of sight without distorting the image in the plane of thebending or, in other words, `which have zero distortion h. together witha predetermined prism power A, suited to correct the ocular defect of anindividual patient.

The data of a prism of thistype may in any instance be found eitherldirectly by means of previously prepared graphs Asimilar to those ofFigs-8 and 9, or by a trial and error method consisting of two mainsteps.

First, a prism i6 (referring to Fig. 12) of given parameters is laid'out and computations are made to determine-whether or not thatparticular set of parameters gives the desired deviation.V Suchcomputations consist of tracingan axial rayV of light i'lfrom a pointi8' representing the center of rotation of the eyethreugh the prism Vi6at the angle I9 whichit is desired to cause the eye to turn ln viewing agiven object 20. This ray returns to, or intersects Athe normal line ofsight 2iv (along'which the eye would view the object a, directly) .at23, the distance of the 4object from the eye. If the ray does notintersect at 23, the parameters are changed until this/ray i1 does meetthe line 2| at the proper distance from the eye. Second, the distortionis determined for the prism which is selected by the first step, bymeans of `tracing two oblique rays 2| 'and 25, having equal angles ofObliquity, from the point i8 representing the nodal point of theeyethrough the base and apex portions of the prism respectively. If thetwo oblique rays are about equal distances from the axial rayl at 26 and21 (the distance of the object from the eye), therevwill be nodistortion of the object. If theA distortion properties of theprismprove to be unsatisfactory, the process must be repeated, taking a prismof a different set of parameters, untill one is found which will satisfyall conditions.

The rays are traced by the method commonly known in the art'of optics astriangulation vByway of example, a prism mms-.thic

concave curvature cf 68.7983 mm. radius prism power of 7.3884

(angle of devianon==4255o from the center of rotation of the eye andperpendicular to a straight axis between the eye and the object, hasbeen found to have a practically negligible distortion. f

'I'he characteristics o1' a series of prisms of this type, in steps ofone A, are given in Table I below.

In making prisms curved as above described, it has been found that theelimination ofimage distortion inthe meridian of the base apex lineofthe prism, is accompanied by a change in the size of the image in thatmeridian so that the image would appear in its approximately correctsize in vthe meridian perpendicular to the base apex line,Y but wouldappear of a different size in the meridian of the base apexline.Therefore, such cylindrical prisms, if usedbefore one eye only, wouldproduce a relative `difference in the shape oi' the two ocular images.When distortlonless prisms of equal power are put before each eye, nodifferences in the relative shape and size of the ocular images areproduced.y While such pairs of cylindrical prisms are of practical use,they have the disadvantage that, even when so used, they make objectsappear broader than high. In order to bring the image back to its properproportions the lenses 6 have also been curved in the planeperpendicular to the baseapex line, as indicated in Fig. ll, so as tochange the size of the image in that meridian. In order that the size ofthe images in both these meridians be exactly the same,'the curvaturesofthe prisms in the two meridians must be slightly different. 'I'hat is,the lens must beof torio form. Table III gives the curvatures in the twomeridians necessary to equalize exactly the size inboth meridians `for aseries of prisms varying by steps of l` prism diopter. I

If the curvatures in the two meridians are made the same, that is if thelens is given a meniscus spherical form, someY differences in the sizeof the images will be produced. These differences are shown for a seriesof prisms in Tables I and n. l

While such 'variations would cause too great a difference between theocular images if a single prism were used before one eye, they would notif equal prisms are placed before both eyes. In practice such types ofspherical meniscus prisms are most useful. Theyalso have the advantageofbeing much more easily and cheaply made.

TABLE I CoNs'rAN'rs or DrsroarroNLEss` P Rrsns Assuming the eye turns totake up prism power first surface of lens is 28.83 mm. from center ofrotation.` of eye Angle between the Prism power' two [aces of the Thick'Colyex Cog-"ex A prism at the ness ra ius ra lus axis' degrees mm. mm.mm.

l 1. 095 2. 95 5l. U6 50. 65 2 2. 190 2. 55/ 50. 66 49. 64 3. 2. 95 49.66 48. 65 4. 373 2. 95 48. 68 47. 67 5. 439 2. 95 47. 73 45. 71 5. 4614. 754 45. 53 43.90 6. 543 4. 75 45. 97 44. 33 7. 623 4. 75 46. 42 44.78 8. 697 4. 75 46. 88 45. 25 9. 766 4. 75 47. 36 45. 73l 10. 669 4. 7547. 78 45. l5

anais:

THE HORIZONTAL MIIBIDIAN AND THE VERTICAL MEBIDIAN First surface of lensis 28.33 mm.

rotation of eye from center of Magnification horizontal percent Magnincation vertical Prism power A percent TABLE III RADII IN THEHORIZONTAI.AND VERTICAL MERIDIANS To PRODUCE THE' SAME MAGNIFICATIONl IN THEHORIZONTAL AND VERTICAL MnnIDIANs First surface of lens is 28.83 mm.from center of rotation of eye Horizontal Vertical Prism wer A r po RiRz Rx R: mm mm mm. mm

45. 53 43. 90 44.00 42.41 45. 97 44. 33 43. 74 42. 16 46. 42 44. 78 43.53 41. S0 46. 88 45. 25 42. 73 4l. Z) 47. 36 45. 73 42. 00 40. 50 47. 7846. 15 41. 23 39. 75

As was mentioned before with reference to Fig. 2, the prism which iscurved in both directions to the' proper degree for avoiding partiallyor entirely all distortion, and bends the line of sight as desired,effects in addition a change of the size of the ocular image in allmeridians. This overall size change is equivalent to the effect of aplane parallel plate of the thickness of the prism at the line of sightand is, therefore, indicated in Fig. 2 by the magnification at obliqueangle zero. If, for example, a different prism correction is given foreach eye, or if a different magnication is required for each eye, forexample due to inherent overall aniseikonia, the magnfication propertiesof the prism must be corrected. For this purpose, according to ourinvention, we place in series with the prisms 6 (Fig. 10) the lenses 9with curves III and II which change the size of the imageback to itsnatural size or to a size desired, without changing the dioptricposition of the image.

These lenses are designed to have no focal power when they are at aspecified ldistance before the eye with an object at a specifieddistance. By the term effective zero power it is meant that the lensesdo not change the vergence of the incident light, that is the object andthe final image are at the same place. A method for calculating'suchlenses is given in the abovev mentioned PatentA No. 1,933,578.

It is evident that corrections of uniformly (as distinguished fromdistortional) meridional aniseikonia can be enacted by introducingcylindrical size changing components, for example by making lens 9toric, or by adding Surfaces having a similar effect. y

In certain cases of ocular defects it may be desirable to provide achange in focus in addition to 'a change in size, and in that lcase apower lens may be added, or a lens I2 (Figs. 13 andr14) may besubstituted for lens 9 of Fig. 10. Lens I2 is of the general type offocus and size correcting lenses likewise described in the above patentand may be designed as a singlelenswith `curves I3 Aand Il changing bothmagnification and size to ridian by the same amount that the curvedprism willchange it in the apex-base meridian. This lens is then groundand finished.

Next, wecompute the curves for the lens 9 or I2 necessary to change thesize ofthe deflected image back to the desired size. If the focus is notto be changed, a lens like the lens Bis used, but if the focus is `tolbe changed, a lens like I2 or an equivalent structureeiecting both sizeand dioptric changes to `predetermined. degrees is used. After thesecomputations have been made and the lens 9 or I2 has,be'en ground Yandfinished, the prism lens 6 and the lens 9.or I2 are mounted in a lensholding means', such `as thefspectacle frame shown, by whichvthey areheld in axed and proper relationwith respect to eachotherk and aresupported in the proper positionon .the face of the wearer.

It will also appear that we have `provided, in 1 this embodiment of ourinvention, a new means of changing the direction of pointing of an eye`without distortion and with controlled magnication. In doing'this wefirst place-before the eye I5 (Fig. 15) a distortionless magnifyingprism Y lens 6, and then place a secondf'lens 9 or I2 before the eye inseries with the first, said second lens having the proper curves.thereon to compensate for the change in the size introduced in theimage. This meansthatthe line of sight is `first bent withoutdistortionbutA with change in size of the image, andrvthatuthe y changein size is then compensated for` 'This order may be reversed by aVcorresponding"change in the curves of the lenses.' f

Accordingly, in Fig. ,points Pi and Pz, at equal distances from thelinefof sightv, represent an object which is imaged. at Pi', P2', whichimage points, due to the function of the distortionless prism, are atequal distances from the deviated line of sight c', the distance P1P2'being equal to distance Pi--Pz due to the effect of size element9,which, as indicated, retains the image plane in the object plane. Itis evident that by imparting a different magnicationtoelement Y9,distance PIL-P2 can be increased or diminished and that, by giving tothe surfaces of 4element 9 unequal curvatures, Vergence power can beintroduced, removing the plane of P1'-Pz from plane P1,Pz. .It isfurther understood that vsuch magup for reading distances from 20 `and2l represent the desired distortion. Examples ofsuch prismatic elementsare Agiven vbelow-in Tables IV, V, and VI, which list series of prismshaving distortion in convenient steps, each series having a constantprism power of one, three and ve A, respectively. In

this case, points P1 and Pz'of Fig. 15 would be unequally spaced inrelation to v' e TABLE IV Drsmarrorz or Smau Pnrsn-Powna 1A Umu r M 1wam 1) ms" For? of 0 o P m A h` curve ion (related (um u d tm, dioptelsto eye) 0. 00 0. 00 K -8. 40 Concave. 0.0015 0.0125 1.54 D0. 0. 0100 0.0250 +0. 00 Convex. 0.0m 0. 0315 +13. 25 D0. 0.0000 0.0500 +2050 D0.

` TABLE v Drsromon or Smau: PmsM-Powrm 3A Bm, Form oi Uma of h 0M-0% AuM-1) cum plrin (rel` Y 0n u d tan dmpters negato 0.a) 0.00 8. 60Concave 0. 0150 0. 025 3. no. 0.0000 0.050 +1.25 convex 0.0450 Y 0.015+5.00 D0. 0 0500 0. 100 +1100 D0. 0. 015 0. 125 +15. 01 D0. 0 000 0.150+20. 50 Do.

TABLE VI Drs'xmnox or SxNaLaPaIsu-Powna 5A 'unal or l (51 1 M 1) Ba For?or curve p m am h' d0 Hand diopters ($19231 0. 0.00 0. 00 -aso concave 00.015 0. 025 -5 15 D0. 0. 0.000 0.050 2. 15 D0. 0. 0. 045 0. 075 +0. l35Convex 1. 0. 050 0. 100 +3. 00 no. 1. 0.015 0125 +0.00 D0. 1. 0.0000.150 +8.88 D0. 1. 0.125 0.115 +1118 D0. 2.00... 0.120 0.000 +14.12 no.2.25 0125V 0.225 +1100- D5. 2.50....---- 0 150 0.250 +2050 D0.

It should be noted that the distortion changes somewhat, although notvery considerably, with changes of the visual. distance, as shown Aby ags. 8 and 9, which are made position, and innite distance vision,respectively. -It may sometimes be advisableto use different-correctionsfor these two distances.V but in most cases computation for one distancewhich may be dominant, concerning desirability of'correction, or for anintermediate distance, for example 1.332D, is fully satisfactory.

' 'Ihe'foregoing tables are computed for light comingfrom infinity. j 1

The second above-mentioned specic embodiment, namelyr the correction ofldistortional aniseikonia Without bending the line of sight, with theaid of so-called Distortion lenses will now be described.

As shown in Figs. 17 and 1.8, a pair of distor- 1 tionless prism lenses6 designed as above described and having curved surfaces 1 and 8, are

mounted in series, respectively, with' a. pair of prism lenses |09having iiat or plane surfaces ||0 and thereon. These lenses aresomounted that the bases of lenses 6 are opposite lthe apices of thelenses |09. By this means, as will readily be apparent, theimage comingto the eye will first be deilected by the distortionless prismv 6. Then,as the image passes through the flat prism 9 it will be deflected in theopposite direction and distorted. `Hence, the deilections cancelling oneanother, only the distortion effected by prism |09 remains. In addition,the image will be magnied.

In the case of this specific embodiment called Distortion lens, theprism powers of the lenses 6 and |09 are made the same, so that the lineof sight enters the eye with no resultant deviation.

It is, however-,clear that by'making the prism powers of the two lenses0 and |09 different, a resultant deviation of any desired amount mayaccordance with the more general aspect of our invention.

If. the prism powers of the two lenses, for example 6 and |09, are madethe same, thenthe the lensesbut without'deviating the line of sight.

It will readily be seen that the prism 6 which has been curved in bothdirections to the proper degree to avoid entirely or partially alldistortion,-

and prism |09 bend the line of sight as desired, but at the same timechange the size of the image seen therethrough in all meridians.Therefore, if a patient required a different distortional corappropriatelens combination, are so designed that they change both size and focusof the image, both by the prescribed amount'. The'procedure of)computati n is analogous to that described a ove.

arranca otherwise the same effect as combinations of dat and curvedprisms, namely, one prism produces a distortion and a deviation, and theother a. deviation opposing that of the iirst, without distortion. r

As already mentioned, it is further possible, according to ourinvention, to combine prisms, both curved or one curved and onestraight, which produce a prescribed amount of` distortion together witha prescribed amount of deviation of the line of sight.

It will also be apparent that we have invented a new means forcorrecting adistortion verror of an eye vwithout with controlledmagnification. -In doing this we rst place before the eye ||9 a fiatprism |00 to obtain the proper amount of distortion to correct for thedistortion of the eye, after which we place a distortionless magnifyingprism lens 6 of the same prismy power as thelens |09 before the eye withits base Lopposite the apex of the lens |09.l

in order to compensate for the deviation intro# duced by the at prismlens 9, and then we place LE i TAB Vn a third lens I I3 or I6 before.the eye in series DIsrolmoN LENsEs-2 Pinsus or EQUAL PRISM withk thelenses |09 and 6 to compensate for the POWER e change inv sizeintroduced by lenses 6 and |09.

una of uM-0% uM-1) Base cum Bm um Form of distortion nl 414,- h1 tan lstpowerk 2nd power prismV coo o. oo 0.00 5A on o 5A on o Fig. 25.'

base. base. 0. 0. 03 0. 05 EA` 0n -3 5A 0n +3 Fig. 26. l

, ase. base. L@ 0. 06 0.10 5A 0n 5A on +6 Do.

. ase. base.v v k 1.50 0. 09 0.15 6A on -9 6A on +9 Do.

base. base.

TABLE VIII Dls'roa'rIoN LEN sas- 2 PBIsMs oF EQUAL PRISM PowEa Iii';d(M-1)% d(M-1) curve oi Base curve of Form of :mien h" Q-4, h d tan lstprism 2nd prism prism (i A Prism) 0.00---. 0.00 0.00 l A on 0 base l Aon 0 base- Frg. 25. 0. 125.-- 0.0075 0.0125 1A0n 1.50baSe 1 A on +6base.; Fig. 26. 0. 250.-- 0.0150 0. 0250 1 Aon 3.00 base 1 A on +12base. Do.

(3 A Prism) 0.00 0.00 0.00 3 A on 0 base 3 A on 0 base Fig. 25. 0.25.--- 0.015 0. 025 3 A on -1.50base 3 A on +3 base.- Fig. 26. 0. 50---.0. 030 0. 050 3 A on 4.50base 3 A On +0 base.. Do. 0. 76---. 0. 045 0.075 3 Aon 6.00 base 3 A 0n +9 base.. D0. 1.00---- 0. 060 0.100 3 A on-7.50 base 3 A on +12 base- Do.

(6 A Prism) I 0.00..-. 0.00 0.00 5Aon0baso.... 5Aon0base Fig. 250.50-.-- 0.03 0.05 5 A on -3 base.- 5 A on +3 base.. Fig. 26 1.00-... 0.06 0. l0 5 A on -6 base" 5 A on +8 base; Do; 1.50.--- (),09 0.15 5 A on-9 base.- 5 A on +9 base- Do.

Recapitulating, the various elements of f this lens combinationmay becomputed as follows:

First, the proper prism power andr base curve for the prism lens |00 isdetermined, so that it will produce the desired distortion. This can be-readily done graphically as indicated, orl by trial e properly fixedand error, or by computation, as discussed hereinbefore. It should benoted that it may be desirable to have a greater amount of distortionthan can be produced by a at prism. In that case, a prism .on a meniscusbase, with the lens turned backwar ,is used. Combinations of this typearegiven in ables VII and VIII.

The next step is the computation of a distortionless prism 6 of the sameprism power as the distortion prism |09 in the manner already discussed.l

Next we compute the curves vfor a lens ||3 or IIB necessary to changethe size of the distorted image back to the desired size. If the focusis not'to be changed, a lens like the lens 3 is used, but if the focusis to be changed, a lens like the lens H6, or equivalent structure, isused. f

After all these lenses have been finished, they are mounted in a lensholding means, such as the spectacle frame shown, by whichthey areheldin relationwith respect to veach other and are supported in the properposition on the face of thewearer, at the distance from the eyes forwhich the lenses were computed.

This'means that lthe-line of sight is bent, the image at the sametimebeing magnified; that the line of sight is bent back to its originaldirec,- tion but distortion is introduced; and that the change in sizeis .then compensated for.

This order may be reversed by a corresponding change in the curves ofthe lenses. i f

Fig. 24, analogous to Fig. 15, illustrates such an arrangement, thedistances of points P1 and'Pz" from axis v, whose direction is notchanged, in' dicating the distortion with reference to the position ofobject P1, P2. Size compensating yelement I3 does not separate objectand image planes.

It will ,be evident that by giving element ||3 appropriate curvatures,any desired lmagniiication can be introduced, and that a distancebetween object and image (in Fig. 24 assumed to deviation of the line ofsight and zoy be in the same plane) can be introduced by giving element||3 a certain vergence power in addition to its magnificationcharacteristic; It is further evident that the magnication and power ingin substance the same as that discussed above with reference to Fig. 15.Such a distortion plus deviation lens .comprising two prism .elementsmay be preferable in cases where considerable distortion is required.

It will be evident that lens series with distortions and given prismpowers that differ in convenient steps (Tables 1V, V,V VI), includingseries with distortion zero (Tables I, II, III) or prism power zero(Tables V'lland VIII) are useful for testing eyes for eikonic andmuscular defects, and within the scope of our invention.

It is to be understood that wherever a magnifying prism and a reducingflens are lcalled for in the foregoing specification vand accompatheprism may as to make the sizeV has been necessary that the lens be suchimage its proper size after its changed by a prism element.

It is further understood that, at least in certain cases especiallyfavorable for such procedure, the entire size and/or dioptriccorrection,

including that provided l It (Figs. l0, 13.20, 22) can be incorporatedin the element. or elements, having the prism eect.

From the foregoing description it will be seen that we have providedmethods and carrying out all the objects of the invention, and that wehave provided means for correcting distortionalaniseikonia and phoriaorfor `correcting distortional errors of the eye without changing thedirection of the line of sight of the eye, or for correcting thedirection of the liney of sight without introducing distortiom and, inall by lenses 9, I2, H3 or cases, at lthe same time controlling eikon'iccon-l ditions other thanl distortional, and the dioptric propertiesofthe image, whenever it should be necessary.

It should be understood'that the present disclosure is for the purposeof illustration only and that this invention includes all modificationsand equivalents which fall within the scope of the appended claims.

We claim:

1. An eyeglass for-correcting ocular image distortion, and deviation ofthe line of sight by introducing given compensatory amounts of prismaticdistortion and deviation, comprising a lens system having surface means,each of said surface means having in one meridian a curvature, and beingspaced relative to the other surface means, forming a prismatic lenssystem ef- Y fectingv said compensatory distortion, said' compensatorydeviation and a certainfsubstantially zero power magnificationxin saidmeridian, and said surface means being curved in a meridian normal tosaid first-mentioned meridian so as to produce in said second meridian amagnification substantially equal to said magnification introduced bythe rcurvatures in said first meridian,

without substantially affecting said compensatory distortion and saidcompensatory deviation.

2. An eyeglass for correcting ocular image distortion, and deviation ofthe line of sight by introducing given compensatory amounts of pris--matic distortion and deviation, comprising a lens element havingsurfaces, each of said surfaceshaving in one meridian a curvature, andbeing spaced relative to the other forming a prismatic lens systemeffecting said compensatory distortion, said compensatory deviation anda certain substantially zero power magnification in said meridian, andeach of said surfaces being curved in a meridian normal to saidfirst-menmeans forV matic distortion and f having in one meridiansaidcompensatory distorl relative to the other forming a prismatic lenssysl tem effecting said compensatory distortion, said compensatoryprismatic deviation and a certain substantially zero power magnificationyin said meridian, and a second lens element having surfaces, one convexand the other concave, each of the surfaces of said second elementhaving a curvature iny a compensation meridian. being spaced relative tothe other and the surfaces Aof* said rst 'lens element and saidcompensation meridian being located withrespect to said firstmentionedmeridian to produce in said compensation meridian -a magnificationsubstantially equal to said magnification.intrcduced by the curvaturesin said first meridianwithout substantially affecting said compensatorydistortion and said .compensatory deviation. y f

` 4:. An eyeglass for correcting ocular image distortion and deviationof the line of sight by intro- .ducing given compensatoryamounts ofprismatic distortion and deviation, comprising alens ele-` ment havingsurfaces, each oijsaid surfaces having in one meridian a curvature andbeing spaced relative to the other to produce a prismatic lens .systemeffecting isaid compensatory distortion,

` said compensatory deviation, a certain Lsubstantially, zero powermagnification in said meridian and a substantially zero power overallmagnification, and each of in a meridian normal to said first-mentionedmeridian so as to produce a cupped lens element. the said curvedsurfaces producing cave, each of said surfaces having curvatures in twomeridans, aligned with said first-mentioned meridiana, and being spacedrelativeto the other and to the surfaces of said first element toproduce without substantial ,change yof v'vergence power a rgivenoverall magnification which, to-

said surfaces being curved in said secondvmeridian a magnificationcounteracting said gether with that of said first element provides an neyeglass with predetermined meridional and overall magnifications. s

5. An eyeglass for correcting ocular image distortion and deviation ofthe line of sight by introducing given compensatory amounts ofprisdeviation, comprising a lens element having surfaces, 'each of 4saidsurfaces a `curvature and being spacedrelative to the other to. producea prisvmatic lens section effecting said compensatory distortion, saidcompensatory deviation, a certain substantially zero power magnificationinj'said meridian and substantially zero power 4overall magnification,and' each 'of said surfaces being curved in a meridian normal to saidfirst-mentioned meridian so as to produce a cupped lens element, thesaid curved `surfaces producing in said second meridian a magnificationsubstantially equal to said magnification introduced'by the curvaturesin said first meridian without substantially affecting said compensatorydistortion and said compensatory deviation, and a second lens elementhaving parallel surfaces one convex and the other concave, each of saidsurfaces having curvatures in two meridians, aligned with saidfirst-mentioned meridians, and being spaced relative to the other and tothe surfaces of said first element to produce substantially withoutchange of vergen'ce power, an overall magnification substantially equalto that'of said first element, providing an eyeglass substantiallylWithout, meridional magnification and compensating the overallmagnification ofsaid first element.`

6. An eyeglassk for correcting deviation of the line of sight withoutocular image. distortion by introducing a given compensatory amount ofprismatic deviation, comprising a lens system having surface means, eachof said surface means being spaced relative to therotl'ier surface meansto form a lens system having said compensatory prismatic deviation inone meridian and each of said surface means having in said meridian 'acurvature producing at said spacing substantially zero'prismaticdistortion anda certain substantially zero power magnification and eachof said surfacemeans being curved in a meridian normal to said prismaticmeridian to form a cupped lens system, the said curved surfacesproducing in said second meridian a lmagnication substantially equal tosaid magnification introduced by the curvatures in said first meridianwithout substantially affecting said zero distortion `and saidcompensatory deviation.

7. An eyeglass for correcting ocular image distortion withoutsubstantially deviating the lineof sight by introducing a givencompensatory prismatic distortion, comprisingI a lens system havingsurface means, each of said surface means having in one meridian acurvature and being spaced relative to the other surface means forming aprismatic lens system effecting a prismatic deviation, said compensatorydistortion and a certain substantially zero power magnification, and asecond lens system having surface means spaced relative toeach other andto the surface means of said first system to produce a prismatic lenssystem effecting in said meridian a prismaticv deviation opposite to andtherefore compensating said prismatic deviation of said first system,and also effecting a certain substantially zero power magnification, thesurface means of at least one of said elements being curved in ameridian normal to said first meridian so as to produce a cupped lenssystem, the said curved surface means producing in said second meridiana magnification substantially equal to said magnification introduced bythe curvatures in said first merid-ian without substantially affecting'said compensatory distortion and said compensated deviation.

8. Spectacles for correcting binocular vision for distortionalaniseikonia of an amount defined by the tested change in magnificationratio withy changing peripheral angle, said spectacles comprising aframe, and two lens systems mounted in said frame before the respectiveeyes, at least one of said systems having surface" means, each of saidsurface means being spaced relatively to the other and having in onemeridian a curvature forming aprismatic lens system, the surface meansof said two systems, respectively, being in said frame spaced from therespective eyes, and each system being formed of lens mepoint toprogressively different dium of a given index of refraction and havingsurface powers computed according to said indices Vand according to saidspacing, with the.

surface means of each of said systems being dependent upon the other,said curvatures and said spacing to effect in said meridian a givendistortion altering the angles subtended, at areference point 'of aneye,by a fan of light rays from object points in a plane through the objectand said point to progressively different amounts,

substantially-in proportion to said distortional aniseikonia. y r

'9., Spectacles for correcting binocular"v vision fordistortional'aniseikonia ofan amount vdefined by the tested change inmagnification ratio with changingy peripheral prising a frame, andtwolens systems mounted in said frame before the'respective eyes, atleast one of said systems havingsurface' means, 'each ofl said surfacemeans being'spaced relatively angle, said spectacles com- 1 to vtheother and having" in-one meridian a 'curvature forming a prismatic lens'system and'each of said surface means beingcurve'd in a meridian normalto said first-mentioned meridian so as to'produce a cupped lens system;the surfaces of said two systems, v'respectively',*being in frame spacedfrom the respective eyes, and each system being formed of lens medium ofa given index ofrefractionand having `surface powers computed accordingto said indices and according to said spacing, with the surface means ofeach of said systems being dependent upon the other, said curvatures andsaid spacing to effect vin said first meridian a given distortionaltering the angles subtended, at a reference point of an eye, by a fanof light rays from object points in a plane through the object and saidamounts, substantially in proportion to said distortional aniseikonia,and also producing a certain substantially zero power in said secondmeridian producing in that meridian a magnificationsubstantially equalto said magnification introduced by the curvature in said first meridianwithout substantially affecting said given distortion. j

10. Spectacles 4for correcting binocular vision for distortionalaniseikonia of an amount defined by the tested change in magnification`with changing peripheral angle and for deviating the direction of atleast one of the lines of sight to a predetermined degree, saidspectacles comprising a frame, and two lens systems mounted in saidframe before the respective eyes, at least one of said systems havingsurface means, each of said surface means being vspaced relative to theother and having in one meridian a curvature forming a prismatic lenssystem, the surface means of said two systems, respectively, being insaid frame spaced from the respective eyes, and each system being formedof lens medium of a given index of refraction and vhaving surface powerscomputed according to said indices and according to said spacing, withthe surface means of'each of said systems being dependent upon theother, said curvatures and said spacing to effect` l1. Spectacles forcorrecting binocular vision said magnification, and said curvature y vbydeviating the direction of at least one ofthe zero distortion, thesurface means oi'.` said two f systems. respectively, being insaid'frame spaced vfrom ,thev respectie eyes,v each system' lbeingformedof lena of a given indexpfrefraction and having'surface powerscomputed laccording to said s indices f and according to said spacing,with the 'surface means of each of said systems being ,dependentupon-the other, said curvatures and said spacing to retain in saidmeridian unaltered the angles subtended, at a reference point of an eye.by a fan of iight rays from object points lin a plane through the objectand said point, and to bend the line of sight of at least one eye` toIsaidv predetermined degree.

12.".Spectacles for (correcting binocular vision for-distortionalaniseikonia of an amount ydefined by the tested change inmagniflcationfwith changing peripheral angle, without substantiallydeviating the direction of at least one of the lines of sight, saidspectacles comprising aframe,

and two lens systems mounted in .said frame beforethe respectiveeyes, atleast one of said systems having one lens element with surface means,each of said surface means being spaced relatively to the other andhaving in one meridian a curvature forming a prismaticlens systemeffecting a prismatic deviation, and a second lens element havingsurface means spaced relatively to each other and to the surface meansof said first element forming a prismatic lens system 'effecting in saidmeridian a prismatic deviation opposite to and therefore compensatingysaid prismatic deviation ofl said first element, the surface means of.said two systems, respectively, being in said frame spaced from therespective eyes, eachsystem being formed 'of lens lmedium -of a givenindex of refraction and having `surface powers computed according Vtosaid indices and according to said spacing, with the surface means ofeach of said systems being dependent upon the other,

said curvatures and said spacing to effect in said meridiana givendistortion altering the anglesY subtended, at a reference point of aneye, by a fan lof light rays from object points in'a plane through theobject and said point to progressively different. amounts,substantiallyin proportion yto Asaid distortional aniseikonia, withoutsubstantially bending the lines of sight of the eyes.

, ADELBERT AM'ES, JR.

GORDON H GLIDDON. KENNETH N. OGLE.

